Many federal and state regulatory schemes require controlling storm water run-off and water quality, such as levels of pollutants on new developments of land. Before land development, an area will likely have included a variety of natural land features, such as sand dunes, grassy hills and wetlands. The natural land features absorb rainwater and infiltrate storm water runoff into the soil to replenish groundwater and streams. Following land development, however, the area might contain impervious surfaces such as buildings, streets, and parking lots that cover the ground and prevent rainfall infiltration. As a result, storm water runoff can accumulate pollutants such as oil and debris, which then flows into a sewer system or other receiving water bodies.
A number of treatment systems are used in the art to manage storm water before it is released to a sewer system or other receiving system. Such systems include but are not limited to bioretention systems. Bioretention systems are a well-known Low Impact Design (“LID”) approach to mitigate the impacts of impervious surfaces and manage the flow of storm water runoff on developed land. The systems utilize soils and both woody and herbaceous plants to remove pollutants, including ultra-fine and dissolved pollutants, from storm water runoff close to their source. The systems mimic the natural (i.e., pre-development) storm water flow from the land.
One type of bioretention system includes standard bioretention cells that employ inorganic and organic materials known in the art. Storm water is collected into a treatment area of the bioretention cell, through which the storm water is filtered as it percolates downward. Other types of bioretention systems include bioretention swales, also known as grassy swales, grassy drainage swales, vegetated swales, or simply “swales.” Bioretention swales are a common and well known way of filtering, treating and/or draining storm runoff or other dirty water that falls on and/or passes over highways, roadways, parking lots and the like. Swales function as soil and vegetation-based filtration systems, removing pollutants through a variety of physical, biological, and chemical treatment processes. In a typical application, a bioretention swale includes a depression in the ground adjacent to a land improvement such as a highway, road, parking lot, subdivision or other similar development. The depression is substantially covered with a layer of grass that has become well rooted and established within the grassy swale. As passing fluid enters the grassy swale from a roadway or parking lot, for example, it is naturally filtered by the layers of the swale.
Another type of treatment system includes manufactured filters, such as a conventional tree box filter, which is also referred to as a tree box planter. Tree box filters are known in the art for controlling runoff from land. In a conventional tree box filter, storm water runoff flows into an in-ground or above ground vault-shaped container with bioretention media, including mulch, and engineered soil. As the tree box filter infiltrates and temporarily stores runoff water, the bioretention media captures particulate matter, including ultra-fine and dissolved pollutants, and allows the treated storm water to percolate through the system. The storm water eventually exists through an outlet in the container into a drainage system or water retention/storage system. Bioretention systems can also include rain gardens, storm water planters, and other types of bioretention cells that help to slow runoff and facilitate infiltration. Yet other examples of manufactured treatments systems can include storm water retention or detention systems or other storm water management systems that allow for storage, infiltration, treatment, filtration, rainwater harvesting, and/or other processing of storm water.
A concern that has emerged is the ability of treatment systems, including the above-described bioretention systems, to process large quantities of fluid during peak flow periods without having backups that result in localized flooding of the surrounding areas. Most treatment systems will have an upper limit for the amount of water that can be filtered at any time, as well as a maximum capacity for the amount of water that can be passed through the system in any event.
For example, a given bioretention swale can be specifically sized to handle the estimated amount of runoff from an adjacent land improvement for a given time period. At the end of that time period, the party responsible for the swale, such as a municipality, highway authority, developer or property owner, will typically conduct a reconstructive overhaul or replanting of the grass layer in the swale, as it is only a matter of time before pollutants and contaminants overrun the grass and topsoil layers of the swale. Frequently, such an overhaul or reconstruction may be needed ahead of schedule, due to the generally incessant flow of chemicals and pollutants from roadways and similar structures that are washed into swales and drainage systems by storms and other runoff events. Such overhauls or reconstructions are costly and time consuming, and additional problems may ensue in the event that they are delayed or needed ahead of schedule. A weak or failing swale may undesirably pass an inordinate amount of pollutants, sedimentation and other debris onward into a subsequent drainage system during the time that it takes to overhaul or replant the swale. In addition, as regulations tighten or various applications require a higher standard of filtration or pollutant removal, many typical swales and other current methods and systems for removing pollutants normally found in storm water runoff, including hydrocarbons, nitrates, and phosphates, may prove to be inadequate.
In addition, although a treatment system may offer removal of ultra-fine and dissolved and dissolved constituents, gross pollutants such as coarse sediment, trash, and debris can reduce system efficiency and increase maintenance needs. The entrance of gross pollutants, such as trash, debris, floatables, and coarse sediments, are known to “clog” the system and thus reduce the overall efficiency. It can also increase the maintenance frequency of typical treatment systems. Accumulation of gross pollutants can also result in backups and localized flooding of the surrounding areas. In some instances, treatment systems may be used with an underground drainage basin system to catch high storm water flows. The drainage basin systems can catch overflow and release the excess fluid flow into underground drain and piping systems. If introduced into the drainage basin system, trash and debris, may also accumulate and be released into the drain and piping systems, along with the overflow storm water.
Accordingly, there exists a need for treatment system that address many or all of the foregoing problems, including a system that can effectively process increased amounts of storm water runoff falling on or passing over highways, roadways, parking lots, and the like. To address storm water flow during periods of peak flow and increase the upper limit for fluid flow, one or more high-flow bypass mechanisms may be implemented needed.
It is also desirable to remove gross pollutants from incoming storm water prior to releasing it to an underground storm water management system. Ideally, a treatment system should pre-treat (e.g., using filtration) water flow from the developed land prior to releasing it. Pre-treatment apparatus that can remove at least some gross pollutants from the treated flows should be incorporated into the bioretention system in order to minimize land usage. The pretreatment apparatus also should be accessible for intermittent cleaning, repair, and/or other maintenance. Thus, it is another objective of the invention to provide a bioretention system that has pre-filtration capabilities to remove gross pollutants from storm water runoff before it is released. It is yet another objective of the invention to provide a flexible and economical design that simplifies the design of construction of storm water drainage systems in a landscape area.